Soil and loam screening apparatus are known in which a screening apparatus includes a frame and a pair of sloping vibratory shaker screens supported within the frame. Generally the frame has a tall end and a short end joined by two sides and has funneling surfaces directed toward the upper shaker screen. Soil or other material to be screened is dumped onto the upper shaker screen, for example, from the shovel of a payloader, falls from the lower end of the upper shaker screen outside of the frame, while the material which is smaller than the screen of the upper frame passes through the upper shaker screen to a lower vibratory screen of smaller opening dimensions which permits coarser material to be discharged at the one short end of the frame and finer material to pass through the lower shaker screen either onto a conveyor belt or within the frame for later retrieval. Such vibratory loam and soil material screening apparatuses are described in U.S. Pat. Nos. 4,197,194, issued April 8, 1980; 4,237,000, issued Dec. 2, 1980; 4,256,572, issued Mar. 17, 1981; and Des. 263,836, issued Apr. 13, 1982 hereby incorporated by reference and which apparatuses are known in the industry as Read Screen-All.RTM. soil separating apparatuses (Read Screen-All.RTM. is the registered trademark of James L. Read, Middleboro, Mass.).
Generally, the pair of shaker screen assemblies in the above-described loam and soil material separating apparatus is secured compression springs and the shaker assembly bounces on the springs in a rotary-type movement. Movement is imparted by the operation of an off balance shaft mechanism secured to the upper and lower shaker mechanisms generally by an off balance flywheel secured to each end of a shaft, which shaft is driven by a hydraulic motor. Generally, the upper shaker screen is composed of a woven wire assembly of typically large diameter wire in order to withstand the impact of soil or another material dumped by a payloader directly onto the upper screen assembly, and which soil material may includes large rocks or other heavy debris, while the screen of the lower shaker assembly is usually of smaller diameter wire and having smaller openings with the diameter of the woven screen and openings selected for the particular separation desired.
While loam and soil material are generally quickly and efficiently separated in the above-described separating apparatus, where the feed material to the apparatus comprises wide a variety of material such as that found in dumps, which would include leaves, paper bags, sticks, as well as sand, soil, rocks, twigs, cans, bottles, domestic and industrial garbage and trash, and construction site debris, the separation of such material becomes more difficult, for example, plastic bags and long twigs tend to become stuck in the upper or lower woven screen assemblies, and thus must be periodically removed to maintain the efficiency of the separation.
There are a wide variety of vibratory screening apparatus employed to screen various, disparate feed-type materials, and which vibratory screening apparatus rather than using woven screens, comprise comb or finger-like members composed of rods arranged in a series of decks over which the feed material is passed to be separated. Typically, the screening decks are arranged in a shingle array fashion, with each deck generally horizontally or slightly downwardly tilted from the horizontal and having a plurality of array of finger or rod-like members projecting from a transverse frame, so as to provide for the desired separation.
One vibratory screening apparatus is described for example in U.K. Patent GB 2 134 415B published Aug. 15, 1984, which describes a screening apparatus with a plurality of replaceable screening decks arranged transversely with finger-like members defining spaces therebetween and which spaces diverge in a direction from the transverse screen portion of the apparatus. In addition, a similar screening apparatus is described in U.S. Pat. No. 4,693,379, issued Sep. 15, 1987, which apparatus includes a plurality of inclined, open ended bars capable of oscillatory movement and formed in a stepped arrangement with one screen located behind the other to provide for the separation of a wide variety of materials. The screening apparatus employs bars of circular, rectangular, prismatic or T-shape profile cross section and zigzag shaped bars for example to prevent the passage of paper sheets through the bars.
It is desirable to provide for the more efficient and effective separation and also sizing of a wide variety of material in a screening apparatus and method so as to provide for both screening and sizing.